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Journals also vary widely in prestige, influence, and impact, and this is reflected in the citation counts to a journal. Essential Science Indicators provides a long-term citation ranking for journals. A comparison with short-term citation behavior can be made by consulting the Journal Citation Reports (JCR) product published by ISI.

Counting method for papers and citations:

Papers are attributed to their journal of publication. All citations received by a paper in a journal are credited to the journal of the cited paper. No restrictions are made on the citing items in compiling the citation counts, other than that they are recorded from Thomson Scientific-indexed journals only.

Time period for counts (cites, papers, cites per paper):

The time period for Essential Science Indicators counts is 10 years, plus partial-year counts for the current year (data is updated six times a year). This means that any papers in the 10+ year period can be cited by any items in that same period. Thomson Scientific database years (the actual years when items are entered into the Thomson Scientific database, which is not necessarily the publication year) are used to define the time periods.

Types of items counted:

Papers are defined as regular scientific articles, review articles, proceedings papers, and research notes. Letters to the editor, correction notices, and abstracts are not counted. Only Thomson Scientific-indexed journal articles or papers are counted.

Journals included:

Journals included for ranking are drawn from the Essential Science Indicators journal set (see complete journal list for Essential Science Indicators) categorized into 22 broad fields. Fields are defined by a unique grouping of journals, with no journal being assigned to more than one field. The Multidisciplinary field contains journals such as Science and Nature which in an article level classification would be assigned to specific fields. This should be taken into account when analyzing the field ranking of an individual scientist, institution, or country.

Citation thresholds:

Journals selected for listing in Essential Science Indicators must meet a cumulative citation count threshold for the 10+ year period. More information about the actual thresholds used in Essential Science Indicators.

The absence of a journal name in Essential Science Indicators means the journal did not meet the citation threshold for the field to which it has been assigned.

Journal Name variations and unification:

Journal names have been unified to reflect name changes or journal mergers over the ten-year period.

Rank orderings:

Journals in the rankings are numbered from 1 to N, depending on the ranking option selected, with no repeated ranks for ties (ties are then ranked alphabetically). Ranking options include citations, papers, citations per paper, and alphabetic. The citations per paper ranking normalizes to some degree for journal size.

See also: Classification of Papers in Multidisciplinary Journals.